A. Field of the Invention
The present invention relates generally to platform installation systems of a temporary nature for supporting workers, and more particularly to an improved platform system for supporting workers beneath a bridge span to permit painting, sandblasting, and other restoration work involving the bridge span substructure to be conducted.
B. Description of the Prior Art
In the maintenance or restoration of a bridge span, for example a highway overpass, it is necessary to provide a platform for supporting workers beneath the span to allow easy access to the substructure of the bridge span, thereby enabling the workers to perform such tasks as sandblasting, painting, and repairing structural elements.
A longtime and widely-used system for erecting a temporary platform beneath a bridge span includes the use of ground-supported scaffold towers bearing a plurality of spaced support beams secured thereto, and rectangular boards fixed on top of the support beams to provide a platform floor surface. This type of system may be undesirable where traffic on a highway traversed by the bridge span must be restricted and/or pass closely by one or more of the scaffold towers. Also, this type of system is impractical where sufficient ground area beneath the bridge span is unavailable, for instance where the bridge span traverses a body of water.
As an alternative to scaffold platform systems of the type described above, suspended platform systems have been developed which are supported by the bridge structure itself. A typical suspended system includes a first group of longitudinally spaced, transversely extending support beams suspended from bridge structural beams on the underside of the bridge span by vertical cables, a second group of spaced support beams orthogonally overlying the first group and fixed thereto, and rectangular boards secured in place on the second group of support beams to provide a suitable platform floor surface.
An enclosed, cable-supported workplace platform for temporary installation beneath a bridge span is taught by Margaritis in U.S. Pat. No. 5,299,655 issued Apr. 5, 1994. The platform of Margaritis includes, in part, opposing sets of outriggers extending from opposite lateral sides of the bridge span, a plurality of spaced support cables each secured to a set of outriggers or to existing bridge supports so that the cables extend parallel to a centerline of the bridge span, an open-link flooring rolled out over the cables and clipped thereto, and a flexible fabric tarp overlying the open-link flooring and clipped to the cables and/or lateral side portions of the open-link flooring. The platform system of Margaritis specifies chain-link fencing for use as flooring, however this results in considerable sagging or flexing of the platform as weight is applied.